Copy sheet for electrostatic printing



Jan. 29, 1963 E. B. RELPH ETAL 3,075,859

COPY SHEET FOR ELECTROSTATIC PRINTING Filed Feb. 20, 1959 Ere. J

INTENSITY 24 SDURCE SOUR E ar/52am mvawroks United States Patent COPY SHEET FOR ELECTROSTATIC PRINTING Earl B. Relph, Des Plaines, Henry A. Dahl, Mount Prospect, and Robert Christiansen, Park Ridge, 111.,

assignors to A. B. Dick Company, Niles, 11]., a corporation of Illinois Filed Feb. 20, 1959, Ser. No. 794,491 1 Claim. (Cl. 117201) This invention relates to a copy process and to elements for use in the practice of same. It relates more particularly to a dry copy process wherein electronic principles are employed in obtaining a reproduction of configurations appearing on an original, and it functions without limitation as to the color or light absorption characteristics of the original.

Briefly stated, it is an object of this invention to provide a new and improved copy process and elements for use in the practice of same.

More particularly, it is an object of this invention to produce and to provide a method for producing copy sheets which are adapted to receive and hold the electrostatic charge transferred to form an invisible image on the surface thereof and which makes use of such image in the development of good and readable copy.

These and other objects and advatnages of this invention will hereinafter appear and for purposes of illustration, but not of limitation, an embodiment of the invention is shownin the accompanying drawings, in which- FIGURE 1 is a cross-sectional view of an electrostatic writing "tube in association with copy sheets embodying the features of this invention;

FIGURE 2 is a perspective view'in' section of one form of copy sheet embodying the features of this invention; and

FIGURE 3 is a perspective view similar to that of FIG- URE 2 showing another form of copy sheet embodying the features of this invention.

Referring first to FIGURE 1 of the drawings, there is illustrated an electrostatic Writing tube including the target structure and copy sheets upon which the image is reproduced. The electrostatic writing tube corresponds to a conventional cathode-ray tube, except for its target. It includes an evacuated envelope having located therein a cathode 12, a control electrode 14, an anode or accelerating electrode 16', a focus coil 18, and a deflection coil 20. The cathode 12 is connected to a negative potential in the operating potential supply 22. The signals are applied to the intensity control grid from a signal source 24. The deflection signals are applied to the deflection coil from a deflection signal source 26. By means of a voltage-dropping resistor 28, the required amount of positive operating potential is applied to the anode 16 and the focus coil 18.

The target member includes a face plate 30 which is at anode potential. Supported within a slot in the face plate are a plurality of insulated wires 32. Each of these wires is separated one from the other by an insulating material, such as glass. The wires are mounted so that one end extends through to the outside face of the tube which is preferably finished to be substantially flat so that the copy sheet 34, coated with a dielectric writing medium, may be passed extremely close to the ends of the wires which are arrayed in a column to receive electrostatic charges. An external plane or conductor 36 is connected to the anodes and extends in parallel spaced relation to the column of wire points as a ground plane. Portions of the wires at the opposite ends extend into the envelope and in the path of the signals directed thereto from the cathode-ray beam.

In operation, the cathode-ray beam which emanates from the cathode is deflected by the deflection signal source to sweep across the portions of the Wires which extend inside of the tube. Whether or not a wire is energized is determined by the intensity of the control signals received from the signal source 24 at the time that the cathode-ray beam is directed upon the wire. Thus, if the deflection signals and the intensity of the control signals being received from a suitable scanning mechanism, such as a facsimile scanner or a television camera, are suflicient, and if the copy sheets 34 are moved in synchronized relation with the scanning speed, a pattern of charges will be deposited on the surface of the copy sheet to form a latent image. When subsequently developed, using well-known electrostatic developing techniques, the latent image will be converted into a visible image corresponding to the original.

It has been found that, for the development of copy of good quality, it is desirable to make use of copy sheets which are capable of accepting the charge transferred directly from the array of wires onto the surface of the copy sheets and to retain the charge on the surface without dissipation either through the copy sheets or by spread to adjacent areas of the copy sheets.

For this purpose, it is desirable to fabricate the copy sheets 34 with a surface 54 in the form of a continuous layer, film or coating of an insulating, dielectric material of low electrical conductivity, and a base 52 characterized by good electrical conducting properties, but with a seal between the dielectric, insulating layer and the conductive base to block passage of any charges from the surface of the copy sheet through the base.

While the desired electrical conductive properties may be provided by the use of a base sheet formed of a metal, it is more desirable from the standpoint of cost and flexibility to make use of a base sheet formed of cellulosic or cellulose derivative materials, as represented by a sheet of paper. The diificulty arising from the use of a paper base sheet stems from the variation in the electrical conductive properties of the paper, depending upon the amount of moisture present in the atmosphere. It has been found that the quality of the image developed on the surfaces of the copy sheets depends greatly upon the electrical conductive properties of the copy sheets. Thus, it is desirable to make use of base sheets formed of paper but which are independent of the relative humidity for the production of copy.

Thus an important concept of this invention resides in a means whereby copy of good quality can be secured independently of the environmental conditions existing, even when use is made of copy sheets formed of a paper base or other fibrous or cellulosic material, and it is an object of this invention to produce and to provide a method for producing copy sheetsin which use is made of paper base sheets and which are relatively insensitive to the amount of moisture existing in the atmosphere, and which are capable of use independently of the relative humidity consistently to produce copy of good quality by the described electrostatic duplicating system,

It hasbeen found, in accordance with one of the concepts of this invention, that copy of good quality can be secured independently of the influence of the relative humidity when the base sheet formed of paper and coated with a dielectric, insulating material is fabricated to contain an electrolyte in the form of a water-soluble monovalent, bivalent, trivalent or polyvalent metal salt which is capable of ionization in aqueous medium. The watersoluble, ionizable salt may be incorporated into the paper base sheet as a component of the slurry of fibers from which the paper base sheet is formed. It is preferred, however, to incorporate the water-soluble, ionizable salt by suitable treatment of the paper after it is formed. For this purpose, the salt may be embodied in solution in an aqueous medium for impregnation of the paper, as

Example 1 by weight potassium chloride 88% by weight water 2% by weight butanol Example 2 by weight potassium chloride 78% by weight water 2% by Weight butanol In the above formulation, the amount of potassium chloride or other water-soluble, ionizable salt may be varied to be present in an amount as little as 3% by weightand up to as much as or by weight for introducing the desired amount of salt into the paper base sheet. Butanol is not essential to the treating composition, but it contributes materially to the penetration of the treating composition into the paper base sheet and the uniform distribution of the salts throughout the base sheet. Instead of butanol, use can be made of other alcohols such as propanol, isopropyl alcohol, ethanol or other polyhydric alcohols, such as glycol, ethylene glycol, glycerine and the like.

Instead of potassium chloride, use may be made of any of the following water-soluble, water-stable, ionizable metal salts in an amount ranging from 125% by weight of the treating composition:

Barium chloride Cupric sulfate Ferric ammonium citrate Ferrous sulfate Sodium sulfate Aluminum sulfate Sodium hypophosphite Potassium nitrate Potassium carbonate Ferric citrate Potassium phosphate Potassium dihydrogen phosphate Potassium bisulfate Sodium carbonate monohydrate Sodium dichromate Sodium citrate Sodium dihydrogen Phosphate Sodium meta silicate Sodium thiosulfate Disodium phosphite It is believed that it is sufiicient when one of the salts 50, or mixtures thereof, is present in the paper base sheet 52 in an amount greater than 0.5% by weight. More than 10% by weight can be incorporated into the base sheet, but the increased cost is not justified by the differences in results.

Copy sheets 34 formed of a surface coating 54 of a good dielectric, insulating material on a paper base sheet 52 containing the water-soluble, water-stable, ionizable salt 50 are capable of use to provide copy of good quality independently of humidity conditions existing and with little, if any, variation in copy quality or color intensity from high humidity to exceptionally low relative humidity during the copy processing. In other words, the high conductivity permanently built into the paper base sheet by the combination to include the water-soluble and ionizable salt nullifies the influence of humidity to the extent that uniform and good performance characteristics will be experienced throughout the described electrostatic duplicating process.

As the dielectric, insulating surface 54, use can be made of continuous coatings or laminates formed of polyethylene, Wax, unmodified or oil-modified alkyd-type resins, nitrocellulose, ethylcellulose, cellulose acetate, shellac, petroleum resins or other natural resins, polyesters, epoxide resins, organo-silicon polymers, polyvinyl acetate, polyvinyl chloride, vinyl chloride-vinyl acetate copolymer, butadiene-styrene copolymer, chlorinated rubber, polyvinyl butyral, styrene-ethylene copolymer, or acrylic acid ester polymers such as polymethyl methacrylate. These can be applied from solvent solution, water solution or aqueous dispersion onto the prepared paper base sheet 52. Application can be made by conventioai coating means, such as spray coating, roller coating, dip coating, air doctoring or the like, in coating Weights of from 2-10- pounds per 3,000 square feet of surface area to provide a continuous layer 54 which effectively seals the pores at the surface of the paper base sheet to block the passage of charges from the dielectric surface through the conductive base sheet. Instead, the described dielectric, insulating cooating may be provided in the form of a film of resinous material laminated onto the surfaceof the paper base sheet, as repersented by the lamination of a film of polyethylene onto the prepared base sheet.

Another technique which may be employed to enhance the electrical conductivity characteristics of the paper base sheet to render the copy sheet insensitive to the existing humidity conditions resides in the treatment of the paper base sheet, with or without the described salts, to incorporate a humectant as a component of the paper base sheet. As employed herein, the term humectant is intended to include such material as the polyhydric alcohols which are not readily evaporated upon exposure to atmospheric conditions. This includes glycerine, sorbitol, and the polyhydric alcohols such as ethylene glycol, polyethylene glycols, triethylene glycol and the polymers of triethylene glycols and mixtures thereof.

Treatment of the paper base sheet to incorporate the humectant is preferably achieved subsequent to the fabrication of the base sheet as by conventional coating or impregnating means. Such means include a dip squeeze process, a roller coating process, spray coating process, or brush coating and the like. The following will represent the formulation of suitable treating compositions which may be used in the practice of this invention.

Example 3 25% by weight glycerine 73% by weight Water 2% by weight butanol Example 4 25% by weight ethylene glycol 73% by weight water 2% by weight butanol Example 5 50% by weight sorbitol 48% by weight water 2% by weight butanol Example 6 10% by weight ethylene glycol 25% by weight sodium formate 65% by weight water It will be understood that when the paper base sheet is processed to incorporate both a water-soluble, waterstable, ionizable salt of the type described anda humectant, the combination of ingredients may be incorporated into a single, composition for treatment of the paper base sheet, as represented by the following examples.

Example 7 24% by weight glycerine 1.7% by weight dibasic sodium phosphate 69% by weight water 4.3% by weight N-propanol Example 8 25% by weight glycerine 63 by weight water 10% by weight potassium chloride 2% by weight butanol In the treatment of the a humectant, it is found humectant retained within impregnation subsequent to the application of the dielectric, insulating coating.

The following are illustrative of compositions which may be employed to fabricate the dielectric coating 54 onto the paper base sheet.

Example 9 Percent Oil-modified alkyd resin (50% solids in xylene- Aroplaz 7424 of Archer-Daniels-Midland) 36.5 Resin (Piccopale 100-Pennsylvania Industrial Chemical Company) 12 Xylene 21 Barium sulphate 30.5

Example 10 Percent Vinyl chloride-vinyl acetate copolymer (Bakelite VMCH 16.7 Barium sulphate 16.7 Acetone 33.3 Xylene 33.3

For illustrations of additional formulations which may be used in the preparation of the dielectric coatings, reference may be made to the copending application of Henry Dahl and Earl Relph, filed concurrently herewith, and entitled Copy Sheet for Electrostatic Printing, Serial No. 794,490, filed February 20, 1959.

Application of one of the foregoing coating compositions can be made by a conventional coating procedure to provide a uniform layer across the base sheet in coat ing weights of between 2 l0 pounds per 3,000 square feet of surface area, followed by an air dry or, preferably, a dry at elevated temperature of from 125250 F. to accelerate the removal of diluents.

In use, the copy sheets prepared in accordance with the teachings of this invention are advanced between the wire array 32 and the ground 36. Advancement is made in synchronized relation with the scanning of the original to transmit a charge from the wire array in the target to the surface of the dielectric, insulating coating on the adjacent copy sheets.

The charge pattern 56 deposited to form a latent image on the surface of the copy sheets is retained on the surface until the image is developed during passage through a developing section 58 wherein the surface is dusted with a powder, toner, or colored resinous substance in particulate form having an opposite electrostatic charge. The applied image is then capable of being permanently set onto the surface of the copy sheet during passage through a fixing section 60 wherein the image is exposed to heat and/or pressure, or vapor, or by combinations thereof, to provide the visible image 62 on the copy.

It will be apparent from the foregoing that we have provided means built into the copy sheet whereby the copy sheets are capable of receiving and retaining an electrostatic charge transmitted to them by the array of wires extending through as a target in the face of a cathode-ray tube without loss of the charge through the base sheet or without dissipation of the charge by lateral migration. It will be apparent that a copy sheet prepared in accordance with the concepts of this invention will embody the desirable characteristics of good electrical conductivity in the base sheet, coupled with a good electrical insulating properties on the surface, whereby copy of good quality can be secured without influence by the amount of moisture existing in the base sheet or the relative humidity conditions in the environment.

It will be understood that changes may be made in the details or construction, arrangement and operation Without departing from the spirit of the invention, especially as defined in the following claim.

We claim:

A copy sheet for use in receiving an electrostatic latent image comprising the combination of a paper base sheet, a continuous dielectric, insulating coating on the paper base sheet, a humectant uniformly distributed throughout the paper base sheet present in an amount within the range of 0.10% to 10.0% by weight of the paper base sheet, and a water-soluble, water-stable, ionizable metal salt uniformily distributed throughout in an amount within the range of 0.05% to 10.0% by weight of the paper base sheet, said percentages being based upon the weight of the paper base sheet.

References Cited in the file of this patent UNITED STATES PATENTS 2,914,403 Sugarman Nov. 24, 1959 

1. A COPY SHEET FOR USE IN RECEIVING AN ELECTROSTATIC LATENT IMAGE COMPRISING THE COMBINATION OF A PAPER BASE SHEET, A CONTINUOUS DIELECTRIC, INSULATING COATING ON THE PAPER BASE SHEET, A HUMECTANT UNIFORMLY DISTRIBUTED THROUGHOUT THE PAPER BASE SHEET PRESENT IN AN AMOUNT WITHIN THE RANGE OF 0.10% TO 10.0% BY WEIGHT OF THE PAPER BASE SHEET, AND A WATER-SOLUBLE, WATER-STABLE, IONIZABLE METAL SALT UNIFORMILY DISTRIBUTED THROUGHOUT IN AN AMOUNT WITHIN THE RANGE OF 0.05% TO 10.0% BY WEIGHT OF THE PAPER BASE SHEET, SAID PERCENTAGES BEING BASED UPON THE WEIGHT OF THE PAPER BASE SHEET. 